1. Field of the Invention
The present invention pertains to the technical field of a fan for forming an air curtain at an opening of a building.
2. Discussion of Background
Such an air curtain is formed by cross flow fans with air flowing across impellers or axial fans. In case of using the axial fans, a structure which has been disclosed in e.g. JP-A-6313603 has been adopted. Specifically, as shown in FIG. 12 of the present application, axial fan units 101 which are respectively constructed to work as an independent fan are arranged in a row to provide a collective fan as a whole. Although it is difficult to modify the entire length of a collective fan in case of using the cross flow fans, the arrangement of the units 101 as just above mentioned allows the entire length to be easily modified by increasing or decreasing the number of the units 101 or adjusting spacing between the units 101.
The air curtain is discharged directly downward or downward at an angle with respect to the vertical direction as needed. The discharging direction of the air curtain is changed by adjusting the direction of outlets of the collective fan. In practice, changing the discharging direction is dealt with by adjusting a mounting angle of the collective fan to a building, or providing rotatable louvers at a downstream side of the collective fan, which is disclosed in the publication.
From the viewpoint that a person who passes through the air curtain in winter is exposed to fast cold air and feels extremely cold, some collective fans have a heater incorporated thereinto to heat the air. Cross flow fans have the same arrangement as a hot air heater adopted thereinto for heating, discharging a heated air curtain. Each guide 102 which is formed as a flow divider has a reflecting plate 103 and a heater 104 incorporated therein to irradiate heat downward even in the axial fan type of the publication as shown in FIG. 13, preventing a person from feeling cold.
The conventional collective fan with axial fans in a row as stated earlier creates some problems. One of them is that it is difficult to take measures to prevent a person from feeling cold. In order to obtain heated air in the arrangement shown in FIG. 13, each unit 101 has to be provided with means for generating heated air though an air curtain itself remains cold and coldness can not be modulated drastically. On the other hand, when the collective fan is installed at a door way and the like of a walk-in refrigerator, it is not necessary obtain heated air. Under the circumstances, it is disadvantageous in terms of cost and production to cope with those two contradictory purposes by providing two types of fans.
Another is that when the collective fan has a heater incorporated therein to obtain heated air, a heater supporting structure and its accessory parts are needed in addition to requirement of a heat-resistant structure, which can not meet the demands for a decrease in cost and companction. Because two rows of air flows are blown out, collective fans for industrial use which are operated by three-phase alternating current has difficulty in the number of heaters in terms of load balance of three-phase alternating current supply. It is difficult to equalize the temperatures of two rows of air curtains.